LONDON — It is the biggest development in this city’s buzzing financial district, and even Olympics-jaded Londoners call it grandiose: two bronze-and-stone towers, connected by sky-bridges atop the ruins of a 2,000-year-old Roman temple.

Bloomberg Place, roughly the size of a Manhattan city block, is the future European home of Michael R. Bloomberg’s company and charity. But it is only one piece of the New York City mayor’s growing British empire.

He is underwriting a major expansion of one of England’s most prestigious galleries, in Kensington Gardens, designed by noted architect Zaha Hadid.

He has the ear of London’s raffish mayor, Boris Johnson, who dispatches aides to City Hall in New York for tutelage in municipal management.

Bloomberg and his aides court the city’s elite, holding expensive dinners for tastemakers and important people on Downing Street. The buzz is so great that one of Prime Minister David Cameron’s chief aides impishly floated the idea of a Bloomberg candidacy — for mayor of London.

As he imagines a more global life for himself after City Hall, unshackled from the 24/7 needs of running New York, Bloomberg — an Anglophile with a taste for English Regency style — is exporting his vast quantities of financial, social, and political capital to this ancient city, where he has long yearned for influence.

Manhattan is home, and Bermuda a weekend escape, but no place has captured the mayor’s imagination like London, a kind of Bloombergian utopia where guns are banned, drivers pay a fee at peak hours, and bicycling is a popular mode of commuting.

The affection, it turns out, is mutual: Bloomberg wrote a blurb for a book written by Johnson.

“Mike’s had a lot of cut-through in Britain,” Johnson said in an interview on a London commuter train last month. “We endlessly try to find ways of entertaining him, but generally speaking, it’s the other way around.”

Advisers to Cameron tried their own version of 3-1-1; Johnson started a volunteer program modeled after Bloomberg’s. Both have dined with the mayor in Manhattan.

“When I’m in New York, I’m treated like a king by Bloomberg, and it’s fantastic,” Johnson said.

Still, any foreign affair has its hiccups. Bloomberg’s attempts to install noisy air conditioners at his $20 million London home have earned the ire of neighbors, prompting local officials to call the plans “totally unacceptable.” And some of his more high-minded policies, like soda limits, have left the natives bemused.

A gallery in the park

Just as he assiduously conquered New York City’s social scene, Bloomberg has, from his earliest days here, relied on parties and philanthropy to propel himself into London’s upper echelon.

He threw himself into the city’s cultural scene, joining the boards of the Serpentine and the Old Vic theater. A public relations firm was hired to make introductions in London society.

In a country where the government often financed the arts, Bloomberg adopted a more U.S. style of corporate giving, stamping his name in museums where he paid for audio guides and sponsoring the Royal Court theater’s “Bloomberg Mondays,” when tickets were sold at a discount.

He bought a box at Ascot, the high-society horse racing grounds, and flew in celebrities by helicopter from London. (Guests received a photograph of themselves drinking champagne with the top-hatted host.)

Even the Royal Family was in his sights. Bloomberg once spent a night at Prince Charles’ home in Scotland, known as Birkhall. The mayor, who keeps luxurious homes himself, later told an aide to Johnson that he had been unimpressed.

“Won’t stay there again,” he said, of the 53,000-acre estate.

Bloomberg has held parties at his two-story apartment on exclusive Cadogan Square, although his mayoralty makes it hard to spend a lot of time there: Bermuda is a two-hour flight, but a trip to London would leave him less than prepared in an emergency. Nowadays, he often spends less than 24 hours at a time in London, preferring to sleep on his private jet.

The distance has not stopped the mayor from trying, on two occasions, to outfit the home with king-size air-conditioning units, an unusual amenity in rainy London.

The plans have met with resistance. Giulia Marsan, a descendant of the founder of Fiat, who lives next door to Bloomberg, told the local planning board that she would “strongly object” to the units, citing noise concerns. An environmental officer agreed, and the board later rejected the plans.

Marsan, in a brief interview, said she barely saw Bloomberg in the neighborhood.

“That’s the hope for everybody in Cadogan Square,” she said. “You never know what’s going on with your neighbors.”

Often, Bloomberg picks other places in which to entertain. He has dined at Le Gavroche, a high-end French restaurant, named for a street urchin in “Les Miserables,” with a $280 tasting menu. On a recent trip, he held a dinner with Louis B. Susman, the U.S. ambassador; Kevin Spacey, the actor; George Osborne, the chancellor of the Exchequer; and Honeysuckle Weeks, a young English actress Bloomberg admired.

Weeks later gushed about the “special dinner” to The Daily Mail. Bloomberg was less impressed: He was disappointed when he learned that Weeks smoked.

“It’s not a timid building”

Bloomberg has long sought a place on the map — literally. Years ago, there was talk that Bloomberg wanted to rename Finsbury Square, site of his company’s office, after himself.

He ended up getting another square instead.

Bloomberg Place, soon to be enshrined on the London map, is currently a mud pit crawling with cranes and bulldozers. By 2016, it will be home to a futuristic campus designed by architect Norman Foster: It is to include a pair of undulating office buildings, pedestrian plazas, spaces for 390 bicycles, and, if the mayor gets his way, branches of New York restaurants.

“It’s not a timid building,” Foster said, on the phone from his home in Switzerland. “It will leave a large impression on London.” (Some neighbors are less generous, calling the development “a bulky, impenetrable mass.”)

The development represents Bloomberg’s future, but he is also buying a piece of London’s past.

In one corner of the development sits the Temple of Mithras, a relic from London’s days under Roman rule. First uncovered in 1954, the temple, a sacrificial altar for an ancient religion, is being restored with Bloomberg’s money.

Last month, a team of 55 archaeologists from the Museum of London were combing the temple site. Their efforts, paid for by Bloomberg, have turned up dozens of artifacts, including coins, pewter bowls, jewelry, and, preserved just where it was found, a human skull.

When the plaza is finished, visitors may descend from Bloomberg Place to view the temple in its original setting. The artifacts, however, become the property of Bloomberg LP, spoils of an expanding modern-day empire.

“We could do a swap”

In 2008, moments after he was elected London’s mayor, Johnson was startled to receive a cell phone call from a U.S. area code. A familiar voice crackled through.

“Mazel tov,” said the mayor of New York City.

Always eager for global impact, Michael Bloomberg, whose mayoralty will end Jan. 1, has not let the 3,500-mile distance from New York prevent him from dabbling in British politics.

When Cameron sought the prime minister’s office in 2010, Bloomberg arranged for top political strategists from SKDKnickerbocker to help out.

Bloomberg and his company have contributed nearly $1.5 million to English candidates and political parties. And he has spoken twice at gatherings of Britain’s Conservative Party, whose center-right, business-friendly views he shares.

The modern London mayor’s office was created in 2000; Bloomberg has offered something of a guide.

“It is very helpful for me politically in London to have such a great example of a municipal authority in New York,” Johnson said.

Johnson sent his new chief of staff to New York for several days of training with Bloomberg’s deputies. Following Bloomberg’s example, he pursued private foundations to pay for pilot projects, and, when he started a volunteer program similar to New York’s Cities of Service, members of Bloomberg’s staff flew across the Atlantic to help implement it.

Some Londoners, tickled by Bloomberg’s nanny-state schemes in New York, compare Bloomberg to Titus Salt, a 19th-century English industrialist who carefully monitored his workers’ vices. (Ale consumption, for instance, was strictly limited.)

“I’m not certain I would try to tell the people of London about the dimensions of their Coke portions,” Johnson said.

As his train neared London Bridge station, Johnson had an idea.

“We could do a swap,” said Johnson, who was born in New York. “When’s he standing down?”